Keratoconjunctivitis sicca (KCS) or “dry eye” is an ophthalmic condition defined by an insufficiency or imbalance of one or more of the ocular fluid components of an eye. Such imbalance may involve aqueous tear fluid, conjunctival mucin, and/or tear fluid lipid. KCS frequently threatens ocular anatomic integrity, often causing conjunctival and corneal erosion. “Dry eye” is a finding in about 25% of Sjogren's syndrome, which most often occurs in women past the age of 45 years. Sjogren's syndrome often detrimentally affects the immune system of the body; thus early detection and treatment is important. It has been estimated that several million persons in the United States alone are affected by KCS. 90% of such KCS cases are due to Sjogren's syndrome. KCS also commonly afflicts several canine species.
One of current diagnosis method for KCS is based on assay of lactoferrin. Lactoferrin, along with lysozyme, tear-specific prealbumin and lipocalin, is one of the major tear proteins synthesized and secreted by the lacrimal gland. It has been reported in the literature that lactoferrin is present in the acinar epithlial cells of both main and accessory lacrimal tissue by immunofluorescence histochemistry (Gillette, et al., Am. J. Ophthalmol 90: 30-37 (1980)). It is also reported that lactoferrin, lysozyme and tear-specific prealbumin are all decreased in the tear of patients with KCS (Jannsen and van Bijsterveld, Clin. Chim. Acta 114:207-208 (1981)). It is generally believed that if the lactoferrin concentration is equal or smaller than 0.9 mg/ml, it is classified as tear-deficiency dry eye.
Currently, there are two tests to assesses the lacrimal gland function by the amount of lactoferrin it produces in the tear film. One is the Lactoplate test, which is an immunodiffusion assay performed in an agarose gel containing rabbit antibody to human lactoferrin. Circular discs of filter paper are placed in the inferior conjuctiva cul-de-sac where they become “soaked” with tears. They are placed on the agar and incubated for three days. While it is accurate in moderate to severe dry eye states, this method is too cumbersome, slow, relatively expensive, and is limited by the experience of the examiner.
Another lactoferrin test is the LactoCard test, which is a solid phase ELISA test requiring only 2 μl of tears. The test is performed by a traumatic application of a 2-μl capilary tube to the lateral inferior tear meniscus to collect tear sample and the lactoferrin concentration in the tear sample is calorimetrically measured by a precise reflectance spectrometer. This test is suitable for office use and has been shown to be as accurate as the Lactoplate in determining tear lactoferrin level. Although the LactoCard test is easily performed in a clinician's office with minimal training, the tear collection by a capillary tube may be invasive or irritating. There is a need for an alternative tear collection device which can be a safer, much faster, and less irritating tear-collecting device.